<template>
  
  <ul class="list">
      <li class="item" v-for="item of letters" :key="item"
       @touchstart="handleStart"
       @touchmove="handleMove"
       @touchend="handleEnd"
       @click="handleAClick"
       :ref="item"
       >{{item}}</li>
  </ul>
</template>
<script>
export default {
    name:'CityAlphabet',
    props:{
        cities:Object
    },
    data(){
        return{
            touchstartus:false,
            startY:0,
            timer:null
        }
    },
    computed:{
        letters () {
            const letters=[]
            for(let i in this.cities){
                letters.push(i)
            }
            return letters

        }
    },
    updated(){
        this.startY=this.$refs['A'][0].offsetTop
    },
    methods:{
        handleAClick (e){
            this.$emit('change',e.target.innerText)
        },
        handleStart (){
            this.touchstartus=true
        },
        handleMove (e){
            if(this.touchstartus){   
                if(this.timer){
                    clearTimeout(this.timer)
                }
                this.timer=setTimeout(()=>{
                    const touchY=e.touches[0].clientY -79
                    const index =Math.floor((touchY-this.startY)/20)
                    if(index >= 0 &&index <= this.letters.length){
                    this.$emit('change',this.letters[index])
                }
                },16)
                
            
            }
        },
        handleEnd (){
            this.touchstartus=false
        }
    }
}
</script>
<style lang="stylus" scoped>
@import '~styles/varibles'
.list
    display:flex
    flex-direction:column
    justify-content:center
    position:absolute
    right:0
    top:79px
    bottom:0
    width:20px
    .item
        line-height:20px;
        text-align:center
        color:$bgColor

</style>
